Experimental infection with Vibrio salmonicida in Atlantic salmon (Salmo salar L.): an evaluation of three different challenge methods

Abstract In testing the efficacy of vaccines for cold water vibriosis in Atlantic salmon a reliable challenge method is essential. Three different challenge methods with Vibrio salmonicida in Atlantic salmon ( Salmo salar L.) were evaluated. The results from 20 batch release tests for vaccines against cold water vibriosis in a test system using intraperitoneal (i.p.) injection were evaluated with respect to the EU guidelines for vaccines intended for fish. Nine bath challenges employed in the development of new vaccine candidates, and one pilot study using a cohabitation challenge, were also included. Review of the test results showed that the i.p. injection was the most reliable method of inducing cold water vibriosis with cumulative specific mortalities in controls above 70% during a three-week observation period post challenge. Nineteen out of 20 challenges fulfilled this criterium. For the bath challenges, only six out of nine challenges succeeded in reaching the same level. In the single pilot study using cohabitation challenge, the disease was transferred from cohabitants to the test fish, but cumulative specific mortalities did not reach the minimum levels stated in the EU guidelines.